Improve consistency of Scala jDBI implicit wrapper
Add OptionResourceMethodDispatchAdapter

This ResourceMethodDispatchAdapter permits resource methods to return an
Option[A], which will either:

    * Produce the contained entity if present, or,
    * Yield a `404 Not Found` response if no value is present.

Much like the `OptionalResourceMethodDispatchAdapter` for Guava's
`Optional` in upstream Dropwizard.